Knee airbags are becoming increasingly widespread in the automotive industry and have two basic tasks: on the one hand they should prevent the knee-shin-areas of the vehicle occupant to be protected from coming into direct contact with the lower area of the instrument panel in case of an accident. Furthermore, knee airbags should prevent the pelvic area of the occupants from being displaced forwards; this is particularly important in the case of occupants who are not wearing seat belts.
The knee airbag is arranged in a housing which is located in the lower area of the instrument panel. It is often desired to locate this housing as far as possible in the direction of the footwell, therefore in the front area of the instrument panel which faces away from the occupant, or in the transition area between the instrument panel and the footwell. However, as the instrument panel is domed in a convex fashion, the knee airbag also has to follow this domed shape, thus showing a “banana shaped” cross-section. In principal this can be achieved through the attachment of outer tethers, which is, however, often not desired.
Generic patent application DE 10 2007 005 304 A1 therefore suggests providing a longitudinal fold and several further folds arranged within this longitudinal fold in a rear section of the airbag skin, in other words in the section which is turned towards the instrument panel, whereby the further folds are secured by means of seams. These further folds achieve a shortening of the ridge of the first fold. When the rear section is under tensile stress—which is the case when the airbag is filled—it assumes a concave shape because of the shortening, leading to assumption of the desired “banana shape”. A knee airbag manufactured in this way basically functions well. However, a disadvantage is that several folds have to be provided which are positioned relatively precisely in relation to each other, which on the one hand makes it difficult to automate manufacture, and on the other hand generally requires a precise final inspection.